In developing security of dwellings, places of business and the like, there is a need for a safety device which will prevent the forcing of an internally located and controlled locking mechanism from the outside of the space for which security is desired. Many locking devices, for example, include an internally located pivotal knob, the function of which is to project a locking bolt into the frame of the door or window and to retract the locking bolt therefrom. It is known to prevent access to such a knob or to lock the knob in fixed position so that unauthorized movement of the locking bolt is not possible.
A number of safety devices of the above indicated general type are known. Some of these devices are shown, for example, in U.S. Pat. Nos. 3,263,462; 3,423,974; 3,826,556; 3,921,423; and 3,933,014.
L. W. Suroff in U.S. Pat. No. 3,263,462 discloses an arrangement in which a retaining device includes a base which is adapted to engage a conventional lock with a press fit and which is provided with inside faces which telescope over a lock actuator to thereby prevent a knob from being rotated by any appreciable amount when a key is inserted from the outside of the associated door.
C. U. Bernsley in U.S. Pat. No. 3,423,974 provides an auxiliary door lock or safety in which a plate is mounted pivotally on a door and is provided with an opening which is adapted for selectively encircling a knob in such a manner as to prevent unauthorized operation of the knob from the outside of the associated door.
In U.S. Pat. No. 3,862,556, A. Moses shows a clamping attachment for a lock-bolt thumb knob for preventing the lock from being opened from the outside. This clamping attachment consists of a U-shaped wire bracket which can be snapped onto the door knob hub which acts as an anchor for the attachment. The closed end of the attachment forms a claw for gripping the wings of the thumb knob and preventing the lock from being opened from the outside by a pass key or other device.
J. R. Hollins shows in U.S. Pat. No. 3,921,423 a door lock assembly including a dead bolt and a knob on the inside of a door for controlling the extension and retraction of the dead bolt. The safety device herein provided is secured to the inside surface of the door and operates selectively to prevent the dead bolt control knob from rotating to retract the dead bolt from an extended position whereby the door is locked. The safety device includes a block from which extends a bar which moves into a position of interference with the aforesaid knob.
A. Moses provides in U.S. Pat. No. 3,933,014 a snap-on clamping attachment for a lock-bolt thumb knob for preventing the lock from being opened from the outside. One of the attachments has elements that can embrace the thumb knob and the connected elements have two extended legs that grip the door knob hub and can bias the attachment to its operative position or hold it inoperative position.